Attempting to PXE boot newer models using USB dongles due to not having a ethernet port will result in failed PXE boot with error "network device not available" or "PXE-E07 - Device not ready."
At least these Dell models will be unable to PXE boot using a USB dongle:
XPS 12 9Q23 XPS 12 9333 XPS 13 XPS 15 Precision Workstation M3800
This may happen with other non-Dell models as well.
"network device not available" or "PXE-E07 - Device not ready"
This is failing due to when the BStrap.efi is running, the NIC UNDI driver is not loaded for the USB NIC.
This behavior was fixed in DS 7.6 HF7 (also in 8.0 codebase) by changing the PXE server to write out *.pxe files under SBS\Images of all data that would be
communicated out on UDP 4011 to client machines.
However, this change is not enabled by default. If you're having this issue do the following on the PXE/SBS servers: